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32 views

Interpretation of Bi-207 decay spectrum

I measured the decay spectrum of Bi-207 as a beta source with scintillation detector and now I am trying to interpret the information given by the spectrum. As far as I know, the Bi-207 nuclei decay ...
-2
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2answers
86 views

Preparing For Jackson Electrodynamics [duplicate]

Hypothetical Scenario: You are an undergraduate physics student who has never taken a course on E&M and you are enrolled in a graduate Jackson electrodynamics course. In general you are good at ...
2
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1answer
73 views

Do pure states actually exist?

Is it possible to ever actually measure something so precisely that it actually collapses to a pure state, or do we really just get arbitrarily close? If a wavefunction never actually collapses to a ...
-4
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0answers
25 views

Could time also be accelerating similar to the Universe's expansion in 3-D? [on hold]

Since the Universe is made up of 3-D space, it's easy for me to visualize that time is just a 4th dimension. It makes sense to think that since the 3 dimensions we can see are accelerating in their ...
0
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3answers
53 views

Difference between eigenstate and basis vector?

My understanding is that any wavefunction can be decomposed into a linear sum of basis vectors, which for momentum are something like sine waves and for position are delta functions. And then ...
1
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2answers
59 views

How can this represent the wave function?

How can $\psi=Ae^{i(kx-\omega t +\phi)}$ represent a plane wave travelling in $+x$ direction? I knew the equation $\psi = A\cos(kx - \omega t + \phi)$. I also know Euler's identity and that the ...
0
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0answers
21 views

Restriction on the value of adiabatic exponent

My instructor stated in his lecture that the maximum value of the adiabatic exponent, $\gamma$, can be 5/3 which is that of a monoatomic gas, but why is this so? He also stated that this can be found ...
2
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1answer
30 views

How do molecules gain kinetic energy from light?

I know that molecules can absorb light through electronic and vibrational excitations, which certainly increase the internal energy of a molecule. This idea is always connected to the quantum theory ...
-2
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0answers
14 views

Planck length and photon [duplicate]

With what probability, i.e. a real number in [0,1],a photon occupies a space of the size of Planck length?
0
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0answers
22 views

Tension due to unequal forces on a massless spring [duplicate]

When a massless spring is pulled by 5N on both sides the tension in the spring is 5N (proved by considering COM at rest and breaking the spring into two springs of 2k each)...what if the forces ...
-2
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0answers
33 views

Photon size vs. Planck length [duplicate]

Another attempt to pose a correct question: with what probability, i.e. a real number in $[0,1]$ photon hits a sphere with diameter the size of Planck length?
1
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1answer
30 views

Some confusion in Drude theory of metals

Discussion on the drude theory of metal usually begin with the case of zero magnetic field so that the force acting on the electrons is just the one from the electric field. But then, this electric ...
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0answers
17 views

The thickness of the hot air layer above a hot metal

I need a simple way to estimate the thickness of the hot air layer above a metal heated up by about 100K above the room temperature. I'm not sure how to go about estimating this. What happens there, ...
0
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0answers
22 views

Magnet oscillation with coils

I am trying to conduct an experiment in which I will try to find the natural frequency of a cantilever. To oscillate the cantilever, I thought I could use a magnet and a current-carrying coil wire ...
1
vote
1answer
37 views

Why does a water jet bend in a static electric field? [duplicate]

The phenomenon is shown for example in this video where a thin water jet is formed by letting water fall from a small hole punched under a plastic cup, and the jet is bent when a charged rod is moved ...
0
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0answers
10 views

What is the physical meaning of a molecular fragment having two appearance energies?

Appearance energies are particularly import when it comes down to mass spectrometers that use electron impact bombardment. They typically denote the quantum energy value for fragmenting the molecule ...
0
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0answers
30 views

How do materials absorb light

I'm curious how light is absorbed in materials. From what I understand, when an electron absorbs a photon, it gets excited to an energy level that is higher than the level it's in and the energy ...
-3
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2answers
77 views

What is the Equation?

I am refreshing my Physics skills and I cannot remember what this equation is. I am hoping that someone can help me. It sort of looks like Stephen Hawkings equation for black holes. $$ S = \frac{C^3 ...
1
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2answers
54 views

How does the underlying symmetry of QCD imply the allowance of a 4-gluon vertex?

Quantum chromodynamics allows for a four-gluon vertex such as this, in a diagram Such a vertex would never be allowed in quantum electrodynamics, which has an underlying U(1) gauge symmetry. I know ...
0
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2answers
64 views

What does strain actually mean?

A problem requires to find the stress in the portions AC and BC of the given figure when a given temperature change takes place. It is mentioned in the solution that total deformation of the ...
0
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1answer
36 views

Simple harmonic motion qsn [on hold]

Have been stuck with this question from classical mechanics under the simple harmonic motion the question is saying that if $$y=a\cos(\omega t)+b\sin(\omega t)$$ show it represents simple harmonic ...
0
votes
1answer
27 views

Energy threshold for photon

I just read https://en.wikipedia.org/wiki/Annihilation#Examples and there is the popular $ e^+e^- \to \gamma \gamma $ reaction described. Is it always possible to produce a $ \gamma $? A photon does ...
0
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2answers
51 views

What is a point object? [duplicate]

I am currently studying Kinematics and there's a little bit confusion about the definition of point object given in my course book NCERT(it is a standard textbook in India) which is as follows : ...
0
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0answers
8 views

Inertial Forces while analysing forces on a Piston in a Slider - Crank Mechanism?

I get that we are analysing the Piston in a Non - Inertial Frame of Reference, but the point of my question is that according to D'Alemberts Principle, whenever an Inertial Force comes in the line of ...
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0answers
14 views

Topos quantum theory and distributive logic

I am reading an introductory review on topos quantum theory https://arxiv.org/abs/1106.5660 where in the motivation part it says (emphasis is mine): As we can see the non realism of standard ...
0
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1answer
44 views

Does the electric field of a charged particle really contribute to its mass? [duplicate]

An electron at rest creates a static distribution of an electric field around it. Wherever the particle moves, it carries or drags the field with itself. Does this electric field contribute to the ...
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0answers
25 views

Flux crossing a portion [on hold]

Please solve ques 3.12 Ans is.5coulomb
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0answers
14 views

Moving Coil Galvanometer' s radial field

How do we produce radial and constant magnetic field for a moving coil galvanometer and also prove that is radial and constant . (i m not asking why do we need it to be radial and its benefits rather ...
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0answers
39 views

What made him think so? [duplicate]

I've been looking into Einstein's theories and was struck with this question. It's contradicting the physics what I've been taught at school. How can mass change with increase in speed and what made ...
0
votes
1answer
22 views

Can classic charge radius formula be used to calculate the radius of muons or taus?

The classic charge radius formula $r$ is used commonly to calculate the radius of electrons(assuming they are spherical). My problem is: can the same formula be used to calculate radii of muons or ...
0
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2answers
58 views

Can a density matrix have more than two dimensions?

It crossed my mind when reviewing density matrices that if you were looking at a composite system consisting of three subsystems, (indexed by three quantum numbers: $<i,j,k|\rho|i,j,k>$) then ...
1
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0answers
38 views

Proton decay - Kamiokande experiment

The Kamiokande experiments measure proton decay using water, i.e. probing the proton in an H-atom. The electron in the H-atom has a nonzero probability at the proton position. It is well known that ...
1
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2answers
42 views

Can we apply ampere's law for a current carrying circular loop

They used the ampere law to calculate magnetic field by a toroid ( assuming perfectly circular coils provinding symmetry and neglecting effects due to helical nature) whis is $μ_0ni$(where $n$ is no ...
1
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2answers
27 views

Is the net force on atomic/molecular constituents of a solid body zero

So my question is this that suppose we consider a solid everyday object, say a spherical stone. Now, if I consider an atom or a molecule of the stone away from the center of the stone, then I can say ...
1
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2answers
63 views

Effect of finite speed of light on timings of events

In relativity when an observer records an event some distance away from him, the timing of the event he measures would be different from what he would measure if he was close to the event as light ...
2
votes
1answer
48 views

Maurer-Cartan form in Physics

I am just reading about the Maurer-Cartan form in the context of Lie Groups, although the mathematical definition: $$\Theta(g)({\bf v}) = (L_{g^{-1}})_{*g}({\bf v})$$ for $g\in G$, $G$ a Lie group, ${\...
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0answers
44 views

What are some websites written by physicists that is worth reading regularly? [on hold]

I am looking for websites written by physicists that I can read in my leisure time. The topic can be on physics or science in general. Ideally, the website should contain a minimal amount of ...
4
votes
1answer
50 views

“Cosmological constant problem” and dark energy

Simply stated: is the "cosmological constant problem" (the discrepancy of about 120 orders of magnitude between measured values of vacuum energy and the ones predicted by Quantum Field Theory) in any ...
0
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0answers
25 views

What's the equilibrium that results if a solid is placed in an empty container at constant temperature?

I'm confused at how to approach this question (in a chapter on phase transitions) since it is so general. My first instinct is to say that is depends on the materials P-T diagram and the temperature, ...
1
vote
3answers
21 views

Units of “mean free time” of a wave/particle

Suppose you have a wave $\phi$ with a complex angular frequency: $$\phi = e^{j\omega t} = e^{j(\omega_R+j\omega_I)t} = e^{j\omega_Rt} e^{-\omega_It} = e^{\frac{-t}{\tau}} e^{j\omega_Rt} $$ Here, $\...
-3
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0answers
37 views

Phase in Simple Harmonic Motion

What is the practical and physical meaning of phase in Simple Harmonic Motion. I don't want to know it by the help of circle projection and using wave graphs.
1
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0answers
38 views

Are states (always) a fundamental notion in QM?

When dealing with quantum mechanics one usually postulates states* as fundamental notions. They form basis of the Hilbert space(H) and are used to compute expected values of observables which we "...
1
vote
1answer
30 views

Getting the Bose-Hubbard Hamiltonian from cold atoms

In the famous paper by Dieter Jaksch, it is shown that the usual Hamiltonian for cold bosonic atoms interacting by s-wave scattering (Equation (1) in the paper): $$ \hat{H}=\int d^3 x\hat{\psi}^\...
0
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0answers
16 views

Primordial dark matter synthesis

In standard cosmology, there is a general picture of: Primordial nucleosynthesis, i.e., when and how, nuclei or elements were formed. It is not quite tested, but it is more or less known where it ...
0
votes
1answer
24 views

Is their a theoretical minimal amout of energy to keep some information?

The goal here is to keep a bit of information $b$ at the temperature $T$ during a time $\delta t$. I don't know if this question makes a lot of sense, considering the diversity of ways to encode ...
1
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3answers
92 views

Schwarzschild Radius of a Galaxy

If an ultra compact/dense Galaxy has a Schwarzschild radius same as it is own radius, how can it be observed from the outside of the Galaxy?
0
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0answers
19 views

Does diffusion of matter (Fick s law) happens at null temperature?

If yes : is diffusion of matter due due temperature ? Why the formula does not include temperature ? Thank you
1
vote
1answer
45 views

Where does the concept enthalpy come from and what does it mean?

I am reading many online references, but I cannot understand where the concept enthalpy comes from and what it represents. The Spanish Wikipedia article states it is the Legendre transformation of ...
0
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2answers
36 views

Beam momentum positive/negative sign

Could anyone explain to me why the momentum of this isostatic beam in $A$ is negative instead of positive? Why isn't it as simple as $+FL-FL/2 = +FL/2$?
0
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0answers
31 views

How much electrical energy can i recover from a heat source at 65 deg Celsius

I am new to the forum and I have been looking around to get a sense of the total waste enegery recoverable from solar cells. We have a pretty sunny climate and the solar cells which covers 600 m$^2$ ...

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